It is well known in the art that polyesters are generally not very stable to the effects of UV radiation. This can be seen by the hazing, property loss, yellowing, etc. that are observed when a polyester is exposed to sunlight, fluorescent lights at short distances for long times, etc. This lack of property stability of polyesters upon exposure to UV light has long limited the uses of polyesters particularly in an outdoor environment.
It is also well known in the art to retard the loss of properties or particularly the development of yellow coloration in exposed articles by addition of a UV absorbing compound (sometimes erroneously called a UV stabilizer) with an extinction coefficient much higher than that of the polymer in question such that almost all of the incident UV radiation is absorbed by said compound rather than the polymer to be stabilized. When the energy absorbed by the UV absorbing compound is harmlessly decayed to the matrix as heat and not transferred electronically to the polymer chain, fragmentation of the chain is thereby suppressed and the properties can be retained for a longer time of exposure. Many such UV absorbing compounds have been developed over many decades of research in this area. It is also well known that many of these compounds are very specific to the polymer systems they are used in.
DE 2,853,631 A1 discloses that copolyesters of polyethylene terephthalate modified with 1,4-cyclohexanedimethanol (CHDM) are desirable for outdoor use but with a low CHDM content they cannot be adequately stabilized by a benzotriazole compound. A later patent, EP 0,595,413 A1 discloses the use of preferably a benzotriazole or a benzophenone compound to unexpectedly enhance the weathering stability of a sheet made from polyethylene terephthalate modified with from 5 to 30 mol % of CHDM. This patent also states that levels as low as 0.5 weight % of the UV absorbing compound may be used for adequate control of color development in the copolyester sheeting.
Certain benzoxazinone compounds are disclosed as ultraviolet absorbers in U.S. Pat. No. 4,446,262. In this patent, the disclosed benzoxazinones are said to be capable of melt mixing with various polymers. Specifically mentioned thermoplastic polymer classes are polyesters, polyamides, polycarbonates, polyolefins, polyesters and polysulfones. Specifically mentioned polyesters are polyethylene terephthalate, polytetramethylene terephthalate and polyethylene 2,6-naphthalate. These are stated to be optionally copolymerized with trifunctional or higher functional comonomers but no mention of coglycols is made for these materials.
The benzoxazinone compounds disclosed in U.S. Pat. No. 4,446,262 are also disclosed in U.S. Pat. No. 5,251,064 as being useful in a reflecting structure consisting of a metalized polyester layer of the same polyesters as disclosed in U.S. Pat. No. 4,446,262. The preferred polyester in U.S. Pat. No. 5,251,064 is stated to be polyethylene terephthalate.
Other UV absorbers that would result from the substitution of various functional groups onto the aromatic ring(s) of the benzoxazinone system are broadly mentioned in U.S. Pat. No. 4,446,262, and more specifically, in U.S. Pat. No. 5,264,539. In U.S. Pat. No. 5,264,539, for example, an oligomer containing benzoxazinone units is blended with a polyester.